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  <title>初始化增量哈希运算上下文</title>
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 <body class="docs"><div id="layout">
  <div id="layout-content"><div id="function.hash-init" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">hash_init</h1>
  <p class="verinfo">(PHP 5 &gt;= 5.1.2, PHP 7, PECL hash &gt;= 1.1)</p><p class="refpurpose"><span class="refname">hash_init</span> &mdash; <span class="dc-title">初始化增量哈希运算上下文</span></p>

 </div>
 <div class="refsect1 description" id="refsect1-function.hash-init-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>hash_init</strong></span>
    ( <span class="methodparam"><span class="type">string</span> <code class="parameter">$algo</code></span>
   [, <span class="methodparam"><span class="type">int</span> <code class="parameter">$options</code><span class="initializer"> = 0</span></span>
   [, <span class="methodparam"><span class="type">string</span> <code class="parameter">$key</code><span class="initializer"> = <strong><code>NULL</code></strong></span></span>
  ]] ) : <span class="type"><span class="type HashContext">HashContext</span></span></div>


 </div>

 <div class="refsect1 parameters" id="refsect1-function.hash-init-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<code class="parameter">algo</code></dt>

     <dd>

      <p class="para">
       要使用的哈希算法名称，例如：&quot;md5&quot;，&quot;sha256&quot;，&quot;haval160,4&quot; 等。
       如何获取受支持的算法清单，请参见 <span class="function"><a href="hash_algos.html" class="function">hash_algos()</a></span>。
      </p>
     </dd>

    
    
     <dt>
<code class="parameter">options</code></dt>

     <dd>

      <p class="para">
       进行哈希运算的可选设置，目前仅支持一个选项：<strong><code>HASH_HMAC</code></strong>。
       当指定此选项的时候，<em class="emphasis">必须</em> 指定 <code class="parameter">key</code> 参数。
      </p>
     </dd>

    
    
     <dt>
<code class="parameter">key</code></dt>

     <dd>

      <p class="para">
       当 <code class="parameter">options</code> 参数为 <strong><code>HASH_HMAC</code></strong> 时，
       使用此参数传入进行 HMAC 哈希运算时的共享密钥。
      </p>
     </dd>

    
   </dl>

  </p>
 </div>


 <div class="refsect1 returnvalues" id="refsect1-function.hash-init-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   返回哈希运算上下文对象，以供
   <span class="function"><a href="hash_update.html" class="function">hash_update()</a></span>，
   <span class="function"><a href="hash_update_stream.html" class="function">hash_update_stream()</a></span>，<span class="function"><a href="hash_update_file.html" class="function">hash_update_file()</a></span>,
   和 <span class="function"><a href="hash_final.html" class="function">hash_final()</a></span> 函数使用。
  </p>
 </div>


 <div class="refsect1 changelog" id="refsect1-function.hash-init-changelog">
  <h3 class="title">更新日志</h3>
  <p class="para">
   <table class="doctable informaltable">
    
     <thead>
      <tr>
       <th>版本</th>
       <th>说明</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td>7.2.0</td>
       <td>当使用 <strong><code>HASH_HMAC</code></strong> 选项的时候，不再支持非加密的哈希函数（adler32，crc32，crc32b，fnv132，fnv1a32，fnv164，fnv1a64，joaat）。</td>
      </tr>

      <tr>
       <td>7.2.0</td>
       <td>
        返回 <strong class="classname">HashContext</strong> 对象，不再返回资源类型。
       </td>
      </tr>

     </tbody>
    
   </table>

  </p>
 </div>

 
 <div class="refsect1 examples" id="refsect1-function.hash-init-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="zlib-encode.example.basic">
    <p><strong>Example #1 增量哈希运算例程</strong></p>
    <div class="example-contents">
<div class="phpcode"><pre><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$ctx&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">hash_init</span><span style="color: #007700">(</span><span style="color: #DD0000">'md5'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">hash_update</span><span style="color: #007700">(</span><span style="color: #0000BB">$ctx</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'The&nbsp;quick&nbsp;brown&nbsp;fox&nbsp;'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">hash_update</span><span style="color: #007700">(</span><span style="color: #0000BB">$ctx</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">'jumped&nbsp;over&nbsp;the&nbsp;lazy&nbsp;dog.'</span><span style="color: #007700">);<br />echo&nbsp;</span><span style="color: #0000BB">hash_final</span><span style="color: #007700">(</span><span style="color: #0000BB">$ctx</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</pre></div>
    </div>

    <div class="example-contents"><p>以上例程会输出：</p></div>
    <div class="example-contents screen">
<div class="cdata"><pre>
5c6ffbdd40d9556b73a21e63c3e0e904
</pre></div>
    </div>
   </div>
  </p>
 </div>


 <div class="refsect1 seealso" id="refsect1-function.hash-init-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="hash.html" class="function" rel="rdfs-seeAlso">hash()</a> - 生成哈希值 （消息摘要）</span></li>
    <li class="member"><span class="function"><a href="hash_algos.html" class="function" rel="rdfs-seeAlso">hash_algos()</a> - 返回已注册的哈希算法列表</span></li>
    <li class="member"><span class="function"><a href="hash_file.html" class="function" rel="rdfs-seeAlso">hash_file()</a> - 使用给定文件的内容生成哈希值</span></li>
    <li class="member"><span class="function"><a href="hash_hmac.html" class="function" rel="rdfs-seeAlso">hash_hmac()</a> - 使用 HMAC 方法生成带有密钥的哈希值</span></li>
    <li class="member"><span class="function"><a href="hash_hmac_file.html" class="function" rel="rdfs-seeAlso">hash_hmac_file()</a> - 使用 HMAC 方法和给定文件的内容生成带密钥的哈希值</span></li>
   </ul>
  </p>
 </div>


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